The invention relates to a method for operating a gas internal combustion engine having a gas mixer, an intake path and an engine having a number of cylinders. The invention further relates to a control system for the internal combustion engine and an internal combustion engine. The gas internal combustion engine further has, in the intake path, a forced-induction unit and a bypass path r bypassing the forced-induction unit. In particular, the gas internal combustion engine is a spark-ignition gas internal combustion engine.
Fields of application for this type of gas internal combustion engine are mobile applications—such as marine engines or utility vehicles and heavy goods vehicles—and also static applications such as local power plants which are in particular advantageously to be configured for a variable gas supply.
U.S. Pat. No. 6,131,552 discloses, in general terms, a fuel control system which can regulate the supply of gas to a mixing chamber as a function of a measured operating state of the engine. The control method of U.S. Pat. No. 6,131,552 A or other purely load-dependent gas meterings prove unsatisfactory even in the case of complex control systems.
Customarily, air consumption is a measure of the gaseous fresh charge of charge air supplied to a combustion engine in a charge mixture, wherein the air consumption also permits monitoring of the quality of the intake system and intake process. The actual air consumption generally represents the ratio of the mass of fresh air in a charge mixture actually supplied to the engine or to a cylinder thereof, during an operating cycle. This real mixture mass is, with reference to the theoretical fresh charge mass, determined from the geometric displacement volume and the theoretical charge density under atmospheric conditions (in the case of naturally aspirated engines) or, in the case of forced-induction engines, in this case the state of the fresh charge downstream of the compressor or downstream of the charge air cooler is taken into account.
Fresh charge supplied to a cylinder is affected by a number of factors such as the valve control times or the opening cross section of the valves. This can in principle be determined by a module for determining the engine forced induction, which is supported by an intake path model. In actual fact, however, only in exceptional cases does the fresh charge supplied to the engine in a charge mixture correspond to the theoretical. Air consumption is not a constant value for an engine, but is greatly dependent on the engine speed and the actual geometric ratios of the intake tract and the combustion space; in order to overcome this dependency it is possible to refer for example to a suitable characteristic map.
Intake path models, in turn, are in principle known in engine controllers in the context of general internal combustion engines, such as in EP 1 398 490 A2. Common to these is the widely adopted fundamental concept for modeling the intake path—in the simplest case as a homogeneous pressurized container in order to detect the dynamic processes in the air path—of modeling the storage behavior of the intake path (also termed suction tube) by means of the filling and emptying methods. In that context, the suction tube is treated as a pressurized container which is continuously filled with air via a throttle flap and out of which the engine sucks air via the inlet valve by means of its suction behavior corresponding to the working rhythm.
However, it has been found that fuel supply for a gas internal combustion engine, in particular in the transient operating range of the internal combustion engine and in the event of variable fuel qualities, is still very much more complex. In particular, it can be seen in the context of gas internal combustion engines, in particular for designing a spark-ignition gas internal combustion engine, that operation in the low-load range and/or in the transient-load range can be problematic.
In the operation of gas engines, the mixture is commonly formed upstream of the compressor of the exhaust-gas turbocharging. At the same time, the intake path between the compressor outlet and the combustion space inlet consists of partially large volumes which thus store or discharge significant masses of mixture. This is in particular the case when, in the event of changes in load on the engine and/or in engine speed, there arise in the individual partial volumes changes in pressure and/or in temperature. As a consequence of a suitable mixture mass formation, however dictated only by the operating point—because this is imprecise in particular due to the partially large volumes—in the case of a gas internal combustion engine, high hydrocarbon emissions (HC emissions) or other raised emissions (NOx, CO, particulates, etc.) as well as low efficiencies are to be expected as a consequence of un-combusted combustion gas.
It is desirable to provide a more advantageous gas operation of a gas internal combustion engine in particular in the transient, in accordance with the load requirements and also the emissions requirements. It is in particular desirable to realize this at least in the low-load range. It is in particular desirable to realize this in the full-load range, i.e. preferably up to 100%.